An electron and a proton are initially very far apart (effectively an infinite d

Question

An electron and a proton are initially very far apart (effectively an infinite distance apart). They are then brought together to form a hydrogen atom, in which the electron orbits the proton at an average distance of 5.08 10-11 m. What is EPEfinal - EPEinitial, which is the change in the electric potential energy?

I got the answer t be positive because its EPEf-EPEi (which is 0). The correct answer is actually negative. Why is that? Why is the change in electric potential energy negative and not positive. Why do you multiply by -k

Explanation / Answer

Given that

charge q1=1.6*10^-19 C

charge q2=-1.6*10^-19 C

distance d=5.08*10^-11 m

now we find the change in the electric potential energy

the change in the electric potential energy =kq1q2/d

=9*10^9*-1.6*1.6*10^-38/5.08*10^-11

=-4.54*10^-18 J

the finial answer is negative because eletron is negative value

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